Equipment is known for the production of foam buns or sandwich boards which consist of a foam core between facings. In the latter case, a so-called double conveyor is used, consisting of a lower and upper conveyor belt. In the case of bun production, the forming foam can rise freely and may be leveled from the top to avoid bulging. In the case of sandwich board production, the two conveyors exert pressure on the forming foam.
A problem which has not yet been satisfactorily solved is the uniform distribution of the reaction mixture in the advance direction and particularly in the transverse direction.
One of the most commonly used application methods is the use of a mixhead which continuously moves from left to right in a line sequence. This method, however, causes the material to accumulate at the edges. The oscillating movement of the mixhead results in high impacts on the turning points. Because of the high velocity involved, these impacts create wear and tear and cause the material to splash. At high manufacturing velocities, the additional problem occurs that the distance between the zigzag lines of the applied mixture becomes too wide.
The use of an inclined table is also well known in the art. It has the advantage that the reaction mixture flowing from the mixhead meets the application surface more gently due to the angle of the inclination. The mixture already partially distributes itself over the operation width on the table. With wider operation width, several parallel mounted mixheads have been used. However, difficulties have been encountered where the individual flows intermix during spreading. Cellular striation and bubbles form in the finished part.
Attempts have been made to level the applied mixture with a rake or a roller by forming a space with the conveyor. This becomes a problem when the space has a wide width. It was found that the transverse distribution does not take place fast enough and that the reaction mixture begins to foam on the edges before the mixture passes the space. This causes non-homogeneous edge zones in structure as well as in density. For this reason, too, the processing of highly reactive systems presents considerable problems.
Therefore, in the continuous production of continuous foam buns and particularly in the production of foam boards or sandwich boards having a foam core, the problem must be solved of improving the mixture distribution over the operation width to such a degree that a satisfactory homogeneity of the finished part is obtained. In doing this, the length of the pouring end or the total length of the equipment should be as short as possible.